import java.util.Scanner;

/**
 * Created by Salted fish
 * Description:
 * User: 24539
 * Date：2021-07-30
 * Time: 13:45
 */
public class Test6 {
    public static void main(String[] args) {
       Scanner sn= new Scanner(System.in);
       int n= sn.nextInt();
        System.out.println(fn(n));
    }
    public static int  fn(int n) {
        if(n == 1 || n == 2) {
            return 1;
        }
        return fn(n-1)+fn(n-2);
    }
}

